Abstract Flash photolysis of aniline derivatives in various solutions has been studied in oxygenated and deoxygenated conditions. Absorption spectra of the triplet states appeared in deoxygenated liquid paraffin solutions, but no transient absorption was observed in the oxygenated liquid paraffin solutions. Transient spectra, due to the cations of the anilines, were observed in deoxygenated ethanol solutions, but none in oxygenated ethanol. In highly polar solvents—acetonitrile, water, and formamide—either deoxygenated or oxygenated, the cation was observed. In the case of oxygenated solutions, the initial yield of the cation was found to be proportional to the intensity of the flash light, indicating that the ionization is a one-photon process. These results, together with the previous findings that the photo-ionization of organic molecules in solutions are caused by the two-step, biphotonic excitation processes strongly suggest that the charge transfer states are formed between the aromatics and the oxygen molecule, either by direct excitation or via the interaction of excited anilines and the ground state of oxygen, and the charge transfer states then lead to the solvated cations and anions in highly polar solvents. The decay of the ions have been found to follow the second order kinetics.